This invention relates to the conversion of certain alkanes containing two unbranched alkyl groups of the C.sub.1 -C.sub.3 range spaced from each other at specific distances on the chain into dihalogenated derivatives in which the halogen is chlorine, bromine or fluorine. The halogenating agent is a C.sub.4 -C.sub.5 tertiary alkyl chloride, bromide or fluoride. The products are dihalides having a halogen and an alkyl substituent at each of two chain carbons which are separated from each other by two other carbon atoms; for example, 2,5-dichloro-2,5-dichloro-2,5-dimethylhexane. These products have utility as intermediates for preparing difunctional derivatives, e.g., diacids, dialcohols or diamides, which are useful as monomers in polymer manufacture.
Hydrogen-halogen exchange reactions between a tertiary alkyl halide, such as t-butyl chloride, and various hydrocarbons containing one or more tertiary hydrogen atoms, wherein an aluminum chloride catalyst has been used, have been described in the prior art for effecting monohalogenation. Such procedure has been shown, for example, by C. W. Kruse, Preprints, ACS Pet. Div., Vol. 12, No. 2, Advances in Petrochemical Symposium, Miami Beach, Florida (April, 1967), and in the following United States patents:
______________________________________ PATENTEE PATENT NO. ISSUE DATE ______________________________________ Schmerling 2,448,156 Aug. 31, 1948 Condon 2,629,748 Feb. 24, 1953 Condon 2,646,453 July 21, 1953 Schneider et al. 2,742,507 Apr. 17, 1956 Gerzon 3,096,372 July 2, 1963 Mahan et al. 3,230,269 Jan. 18, 1966 Kruse et al. 3,247,277 Apr. 19, 1966 ______________________________________
However, none of these references teaches the preparation of dihaloalkanes by means of a hydrogen-halogen interchange reaction.
While sulfuric acid generally would be a more desirable catalyst than aluminum chloride for commerical practice, references to its use as a catalyst for hydrogen-halogen exchange reactions are more scarce. The following references on this subject appear to be the most pertinent:
U.S. Pat. No. 2,744,940, issued May 8, 1956, Herman Pines, discloses the monochlorination of various alkylcyclohexanes by means of tertiary butyl chloride and employing strong sulfuric acid as catalyst. Under the reaction conditions taught, monochlorination of the starting naphthene occurs but no dichloro products are produced.
U.S. Pat. No. 2,810,001, issued Oct. 15, 1957, Herbert K. Wiese, discloses the reaction of methylcyclopentane with tertiary butyl chloride at -10.degree. to 25.degree.C. utilizing 85-100% H.sub.2 SO.sub.4 as catalyst. The patent teaches that monochlorination of the methylcyclopentane at the tertiary carbon atom first occurs but that the monochloro product inevitably further reacts, by undergoing a condensation reaction with liberation of HCl, to produce dicyclic monochloro products.
U.S. Pat. No. 2,831,036, issued Apr. 15, 1958, Herbert K. Wiese, discloses the monochlorination of branched C.sub.6 -C.sub.8 isoparaffins having one or more tertiary carbon atoms by reaction with tertiary butyl chloride at -25.degree. to 25.degree.C. employing 85-100% H.sub.2 SO.sub.4 as catalyst. The patent gives no indication that dichlorides can be produced in this type of reaction.